In an alkaline battery an air electrode cathode and a metal anode, such as iron or zinc, are spaced apart in an alkaline solution. Air diffuses into the air electrode where oxygen is reduced, releasing hydroxide ions into the alkaline solution, resulting in the generation of electricity. While this type of battery is rechargeable, it can be used only in alkaline solutions. Since seawater is neutral, or nearly neutral, alkaline batteries will not function with seawater as the electrolyte.
Batteries commonly used with seawater as the electrolyte employ an anode of magnesium and a cathode of copper chloride or silver chloride. These batteries function according to the following equations:
______________________________________ At the anode: Mg + 2Cl.sup.- .fwdarw. MgC1.sub.2 + 2e.sup.- At the cathode: 2MCl + 2e.sup.- .fwdarw. 2M + 2Cl.sup.- Overall reaction: Mg + 2Cl.sup.- .fwdarw. MgCl.sub.2 ______________________________________
where M is copper or silver. These batteries are generally heavy and require a large amount of space. For example, an Mg/CuCl battery that can generate one watt year might be 8 to 81/2 feet long, about 9 inches in diameter, and weigh more than 100 pounds. Moreover, that battery has limited flexibility in design and is generally limited to this elongated shape.
In order to power underseas detection and monitoring devices, it is necessary to have small, light-weight batteries that will function reliably for at least one year, and that can be made in shapes compatible with the remainder of the device.